U.S. patent application number 09/827209 was filed with the patent office on 2001-11-08 for emulsion ink for stencil printing.
Invention is credited to Ogawa, Hiroyuki, Okuda, Sadanao, Yamada, Hiromichi.
Application Number | 20010037749 09/827209 |
Document ID | / |
Family ID | 18618548 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037749 |
Kind Code |
A1 |
Ogawa, Hiroyuki ; et
al. |
November 8, 2001 |
Emulsion ink for stencil printing
Abstract
A water-in-oil (W/O) emulsion ink for stencil printing is
provided which is prevented from pigment aggregation and thus
excellent in ink fixability, high in printing density and less
declining in printing density even after printing many sheets. The
emulsion ink has a ratio by volume of the water phase to liquid
components of the oil phase (i.e., volume of water phase/volume of
the liquid components of oil phase) in a range of 1.0 to 3.5,
preferably 1.0 to 3.0 at 23.degree. C. The liquid components of the
oil phase may be composed of a resin, a solvent and a surfactant.
The oil phase can contain a pigment at a ratio by volume of 0.19 or
less to the total volume of the oil phase. The pigment preferably
has an average particle size of 0.02 to 1.5 (.mu.m). The water
phase preferably has an average particle size of 0.1 to 1.0
(.mu.m). The ink is suitable for containing particles of organic
pigments with non-uniform shapes and a large average particle size
like copper phthalocyanine blue and diaxazine violet.
Inventors: |
Ogawa, Hiroyuki;
(Ibaraki-ken, JP) ; Okuda, Sadanao; (Ibaraki-ken,
JP) ; Yamada, Hiromichi; (Ibaraki-ken, JP) |
Correspondence
Address: |
Pillsbury Madison & Sutro LLP
Intellectual Property Group
Ninth Floor, East Tower
1100 New York Avenue, N.W.
Washington
DC
20005-3918
US
|
Family ID: |
18618548 |
Appl. No.: |
09/827209 |
Filed: |
April 6, 2001 |
Current U.S.
Class: |
106/31.26 ;
106/31.6; 106/31.65 |
Current CPC
Class: |
C09D 11/0235
20130101 |
Class at
Publication: |
106/31.26 ;
106/31.6; 106/31.65 |
International
Class: |
C09D 011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 2000 |
JP |
2000-105129 |
Claims
1. A water-in-oil (W/O) emulsion ink for stencil printing, having
an oil phase and a water phase, which has a ratio by volume of the
water phase to liquid components of the oil phase (i.e., volume of
water phase/volume of the liquid components of oil phase) in a
range of 1.0 to 3.5 at 23.degree. C.
2. An emulsion ink for stencil printing, according to claim 1, in
which said ratio is in a range of 1.0 to 3.0 at 23.degree. C.
3. An emulsion ink for stencil printing, according to claim 1, in
which said liquid components of the oil phase are composed of a
resin, a solvent and a surfactant.
4. An emulsion ink for stencil printing, according to claim 1, in
which said oil phase contains a pigment in addition to said liquid
components, and the pigment content is 0.19 or less as a ratio by
volume to the total volume of the oil phase.
5. An emulsion ink for stencil printing, according to claim 4, in
which said pigment has an average particle size of 0.02 to 1.5
(.mu.m).
6. An emulsion ink for stencil printing, according to claim 1, in
which said water phase has an average particle size of 0.1 to 1.0
(.mu.m).
Description
[0001] This invention relates to an emulsion ink for stencil
printing, particularly an emulsion ink for stencil printing
excellent in ink fixability, high in printing density and less
declining in printing density even after printing many sheets.
[0002] The heat sensitive stencil printing system recently allows
high grade prints to be obtained readily and quickly since the heat
sensitive stencil making technique in which a thermal printing head
is used as a perforation device with digitized image processing has
been adopted. Therefore, the system has been increasingly noticed
as convenient information processing terminals.
[0003] The stencil printing system has a feature of good and simple
operability that requires no skilled operator, compared with
offset, gravure and letterpress printing systems. In other words,
the stencil printing system is advantageous in that no skill is
required for operation and that no special work such as machine
washing is required after completion of use. Thus, the stencil
printing system does not require any specialist for operation, but
is very suitable for printing a relatively small number of
sheets.
[0004] Furthermore, in the heat sensitive stencil making technique
using a thermal printing head, size of perforations in a stencil
has been standardized, thereby facilitating control of transfer
amount of ink, compared with the conventional stencil making
methods in which infrared light or xenon flash was used as a heat
energy source. Therefore, the possibility that such problems as
set-off and blurring occur due to excessive ink transfer has
decreased, and the image grade has improved dramatically.
[0005] As described above, the stencil printing system is
advantageous in that printing speed is high similarly to the
offset, gravure and letterpress printing systems, and also that it
is easy to operate and can be installed as an office machine like
PPC and ink jet printers. So, the stencil printing system has
expanded its use rapidly.
[0006] For enhancing the image grade, it is proposed to improve
fixability of ink onto paper and achieve a higher density of images
by adding an oil-soluble dye or a mixture of an oil-soluble dye and
a pigment, as a colorant, to the oil phase of a water-in-oil (W/o)
emulsion ink (JP-A-06-9912), to produce a toned ink free from color
separation by adding a water-soluble dye to the water phase
(JP-A-05-117565), to produce an ink high in image density and good
in fixability by adding 5.0 to 12 wt % of a pigment to the ink
(JP-A-09-328645), to prevent set-off by letting an emulsion ink
contain solid particles or waxes of, for example, a polyamide or
polystyrene with an average particle size of 8 to 30
.mu.m(JP-A-06-116525), to improve fixability on paper and storage
stability by keeping an average particle size of pigments dispersed
in the oil phase in a range of 0.15 to 0.4 .mu.m (JP-A-07-179799),
and so on.
[0007] These proposals are intended to improve the printing grade,
but if the pigment content is increased to raise the printing
density, it often happens that pigment aggregation occurs in the
water-in-oil (W/O) emulsion ink. If this phenomenon occurs, it
often happens that the color expected from the corresponding
pigment content is not obtained, thereby causing the printing
density to decline.
[0008] Furthermore, the pigment aggregation in a water-in-oil (W/O)
emulsion ink depends upon dispersion state of pigments. Pigments
poor in dispersibility such as phthalocyanine pigments including
phthalocyanine blue and phthalocyanine green and dioxazine pigments
are large in average particle size and contain numerous non-uniform
coarse particles. If such pigments are used, the pigment
aggregation is apt to occur in the aforementioned water-in-oil
(W/O) emulsion ink.
[0009] If the pigment aggregation grows to form large lumps, it can
happen that perforations of a stencil sheet are clogged. With
recent increase in resolution of thermal heads, pigments are
required to be still smaller than 30 (.mu.m) in particle size. It
is, therefore, increasingly necessary to prevent the pigment
aggregation as far as possible for preventing the clogging of the
stencil sheet, while ensuring the ink fixability and keeping the
storage stability.
[0010] For improving the storage stability, it is proposed to
obtain an ink excellent in storage stability and low in temperature
dependence by treating a water-in-oil (W/O) emulsion ink at a high
shear rate using, for example, stirring blades or rotor stator in
the production of the ink (JP-A-06-192606), to achieve the
fixability on paper and the storage stability by keeping the
particle size of the emulsion of the water phase at 10 .mu.m or
less and the average particle size of the pigment dispersed in the
oil phase at 0.4 .mu.m or less (JP-A-07-179799), and to effectively
decrease the rise of ink viscosity during storage at high
temperature by keeping the sum of the water phase particles content
and the carbon content of a water-in-oil type emulsion ink at 72 wt
% or less based on the total weight of the ink (JP-A-09-328645).
However, if the particle size of the emulsion is kept too small for
making the emulsion stable, it in turn can happen that the pigment
aggregation occurs.
[0011] On the other hand, for water-in-oil (W/O) emulsion inks for
stencil printing, it has been a general practice to keep the ratio
of the water phase weight to the oil phase weight high (many
proposals are presented, for example, in JP-A-61-255967,
JP-A-04-132777, JP-A-04-288375, JP-A-05-93161, JP-A-06-33007,
JP-A-06-107998, JP-A-07-150091, JP-A-10-245516, etc.). However, if
the weight ratio of the water phase is raised, it can also happen
that the pigment aggregation occurs.
[0012] In an emulsion containing a pigment in the oil phase, it
seems that the pigment aggregation cannot be prevented even in
reference to the ratio by weight of water phase/oil phase. In view
of this, the object of this invention is to effectively prevent the
pigment aggregation in reference to another indicator.
[0013] To achieve the above object, the inventors have studied
intensively the physical properties of emulsion inks in reference
to various indicators, and as a result, have found that if the
ratio of the volume of the water phase to the volume of the liquid
components of the oil phase (i.e., volume of water phase/volume of
liquid component of oil phase) is referred to as an indicator, it
is possible to produce an emulsion ink for stencil printing, which
is excellent in printing grade such as printing density and
fixability but does not cause perforated stencil sheets to be
clogged with coarse pigment particles or aggregated pigments even
after many sheets have been printed. Thus, this invention has been
completed.
[0014] This invention provides an emulsion ink for stencil
printing, which is a water-in-oil (W/O) emulsion ink having an oil
phase and a water phase, characterized in that the ratio by volume
of the water phase to the liquid components of the oil phase
(namely, volume of water phase/volume of liquid components of oil
phase) is in a range of 1.0 to 3.5 at 23.degree. C.
[0015] In the water-in-oil (W/O) emulsion ink used for stencil
printing, the addition amount of the water phase has been generally
set in a higher proportion. The reason is that it contributes to
improvements of various properties by way of keeping the viscosity
change due to the ink temperature change small, raising the ink
penetration rate, enhancing the structural viscosity of the ink,
preventing the ink from flowing out of the printing machine, and
lowering the spinnability of the ink when the printing drum is
separated from a printing medium. Therefore, most of the
conventional inks have high water contents.
[0016] However, it was found that if the water content is made
higher than a certain level in a water-in-oil (W/o) emulsion
containing a pigment in the oil phase thereof, the pigment
aggregation occurs. In general, the state of the maximum water
content corresponds to the closest packing in terms of volume.
However, the closest packing includes hexagonal closest packing and
cubic closest packing, and it is actually unknown which of the
closest packing patterns occurs in each water-in-oil (W/o)
emulsion. Furthermore, in the idea of the closest packing, the
packed particles, namely the water nuclei in case of a water-in-oil
(W/O) emulsion, are assumed to be perfect spheres having the same
particle size. So, the optimum water content of a water-in-oil
(W/o) emulsion ink cannot be decided in reference to the
theoretical value. The inventors made experiments of actual
water-in-oil (w/o) emulsion inks using the volume ratio as an
indicator, and as a result, found that if the ratio of the volume
of the water phase to the volume of the liquid components of the
oil phase (i.e., volume of water phase/volume of liquid components
of oil phase) is larger than 3.5 at 23.degree. C., the pigment
contained in the oil phase aggregates to form coarse particles, and
consequently the pigment aggregation causes the decline of color
development efficiency, the decline of fixability and the clogging
of stencils with aggregated particles. It was also found that if
the ratio by volume of the water phase to the liquid components of
the oil phase (i.e., volume of water phase/volume of liquid
components of oil phase) is lower than 1.0, the ink is not suitable
for stencil printing since improvements of temperature
adaptability, penetration rate, structural viscosity, flowing-out
of the printing machine, and spinnability as mentioned above become
small. A preferable range of the ratio by volume of the water phase
to the liquid components of the oil phase is 1.0 to 3.0.
[0017] In this invention, it is preferable that the average
particle size of the water phase is 0.1 to 1.0 (.mu.m). Since
spaces of the continuous oil phase depend on particle size of the
water phase, the pigment aggregation depends on the average
particle size of the water phase. If the particle size of the water
phase is large, the oil phase is not fractionalized, allowing
spaces where pigment particles can exist, and thus the pigment
aggregation is unlikely to occur. However, if the particle size of
the water phase is small, it is considered that the spaces where
pigment particles can exist are fractionalized, and pigments with a
large average particle size are likely to aggregate. From this
point of view, in this invention, it is preferable that the average
particle size of the pigment is 0.02 to 1.5 (.mu.m). Furthermore,
if the pigment content in the oil phase is large, the pigment
aggregation tends to be liable to occur. So, in this invention, it
is preferable that the pigment content is 0.19 or less in terms of
a volume ratio to the total volume of the oil phase.
[0018] The emulsion ink of this invention preferably comprises
about 10 to 50 wt % of an oil phase and about 90 to 50 wt % of a
water phase, more preferably, about 25 to 50 wt % of an oil phase
and about 75 to 50 wt % of a water phase, and the ink can be
produced by dropwise adding the water phase with stirring to the
oil phase for emulsification.
[0019] In this invention, the oil phase contains liquid components
including a resin, a solvent and a surfactant as well as a
pigment.
[0020] The resin is added in order to improve wettability between
the solvent and the pigment and keep the resin and the solvent well
adsorbed by the pigment, thereby improving storage stability of the
emulsion ink and preventing the system of ink from becoming out of
balance even after the ink has been allowed to stand for a long
time. It is also added for the purpose of improving fixability of
the colorant in the ink onto paper or improving finish of prints.
Examples of the resin include alkyd resins, phenol resins, maleic
resin, petroleum resin, etc. Among them, an alkyd resin is
especially preferable since it is highly effective for improving
wettability to the pigment. The alkyd resin may be one which has
been treated for eliminating low molecular components therefrom,
for the purposes of improving stability of the emulsion and
eliminating odor.
[0021] Examples of the solvent include petroleum solvents such as
olefin hydrocarbons, liquid paraffin and aromatic hydrocarbons,
vegetable fats such as coconut oil and palm oil, vegetable oils
such as olive oil, castor oil and linseed oil, synthetic oils, etc.
These solvents may be used singly or in combination of two or more.
Addition amount of the solvent can be properly selected to ensure
that viscosity of the oil phase is adjusted to a desired level.
Today, in view of safety to be secured, it is desirable that the
solvent is selected considering content of aromatic components and
content of volatile components. Furthermore, the solvent should be
selected, sufficiently considering solubility of the resin used, so
as to attain a stable emulsion system that is low in dependence of
viscosity on temperature and is less likely to cause separation of
the solvent even if the ink is allowed to stand in a printing
machine. Moreover, to enhance solubility of the resin, a dissolving
aid can also be added.
[0022] Examples of the surfactant include anionic surfactants such
as metallic soaps, sulfuric esterification salts of higher alcohols
and sulfuric esterification salts of polyoxyethylene adducts,
cationic surfactants such as primary to tertiary amine salts and
quaternary ammonium salts, nonionic surfactants such as esters
between polyhydric alcohols and fatty acids, nonionic surfactants
such as polyoxyethylene ethers of fatty acids, polyoxyethylene
ethers of higher alcohols, alkyl phenol polyoxyethylene ethers,
sorbitan fatty acid esters, polyoxyethylene ethers of polyglycerol
fatty acid esters, polyoxyethylene ether of castor oil,
polyoxyethylene ether of polyoxy propylene and alkylolamides of
fatty acids, and the like. These may be used singly or in
combination of two or more. Addition amount of the surfactant can
be decided considering molar concentration of the surfactant
concerned, area of interfaces between the water phase and the oil
phase, and, as the case may be, area of interfaces between the oil
phase and solids such as pigments.
[0023] Examples of the pigment are colorants including organic
pigments such as insoluble azo pigments, soluble azo pigments,
phthalocyanine blue, dye rakes, isoindolinone, quinacridone,
dioxazine violet and perinone-perylene, and inorganic pigments such
as carbon black and titanium dioxide, as well as extender pigments
such as terra abla, talc, clay, diatomaceous earth, calcium
carbonate, barium sulfate, titanium oxide, alumina white, silica,
kaolin, mica and aluminum hydroxide.
[0024] In addition, for example, a pigment dispersing agent, an
antioxidant, and another auxiliary agent including a compound
mainly containing a wax for adjusting flowability can be added to
the oil phase of this invention to such an extent that formation
and stability of the emulsion are not impaired.
[0025] In this invention, the water phase is composed of water, an
oil-in-water (O/W) emulsion of resins, a water-soluble resin, a
wetting agent, an electrolyte, an antioxidant, and the like.
[0026] Examples of the oil-in-water (O/W) emulsion of resins
include emulsions of resins including polyvinyl acetate,
ethylene-vinyl acetate copolymer, vinyl acetate-acrylic ester
copolymers, polymethacrylic esters, polystyrene, styrene-acrylic
ester copolymers, styrene-butadiene copolymer, vinylidene
chloride-acrylic ester copolymers, polyvinyl chloride, vinyl
chloride-vinyl acetate copolymer, polyurethane, and the like.
[0027] Examples of the water-soluble resin include polyvinyl
alcohol, methyl cellulose, carboxymethyl cellulose, hydroxyethyl
cellulose, polyvinyl pyrrolidone, polyethylene-polyvinyl alcohol
copolymer, polyethylene oxide, polyvinyl ether, polyacrylamide, gum
arabic, starches, water-soluble polyurethane, etc. Addition amount
of these resins is preferably 1 to 20 wt %, more preferably 2 to 10
wt %, as solid content based on the total weight of the emulsion
ink. If the amount is more than 20 wt %, it can happen that the ink
forms a film at perforations of the stencil and inhibits passage of
the ink in case where the ink is allowed to stand for a long time
on a stencil.
[0028] Examples of the wetting agent include polyhydric alcohols
such as ethylene glycol, sorbitol and glycerol, and polyethylene
glycol.
EXAMPLES
[0029] This invention is described below more particularly in
reference to examples, but is not limited thereto or thereby. In
the following examples, "parts" means "parts by weight".
Example 1
[0030] A water-in-oil (W/O) emulsion ink was prepared in accordance
with the formulation shown in Table 1. First, a colorant (copper
phthalocyanine blue) and an alkyd resin were dispersed using a bead
mill. To the dispersion, spindle oil, AF-5 Solvent (produced by
Nippon Oil Co., Ltd.) and sorbitan monooleate were added, to obtain
an oil phase.
[0031] Furthermore, a water phase obtained by adding ethylene
glycol and magnesium sulfate to ion exchange water was gradually
added to the oil phase, and the mixture was stirred for
emulsification, to prepare a water-in-oil (W/O) emulsion ink for
stencil printing.
[0032] Specific gravity of the liquid components (components other
than the colorant) of the oil phase and specific gravity of the
water phase were each measured using a pycnometer at 23.degree. C.
Furthermore, the true specific gravity of the colorant was measured
according to immersion method using a specific gravity bottle.
[0033] Average particle size of the colorant was measured by
diluting the oil phase containing the colorant with an organic
solvent and using a laser diffraction type particle size
distribution analyzer (SALD-2000A produced by Shimadzu Corp.).
[0034] Average particle size of the emulsion was obtained by
photographing the emulsion particles using a scanning electron
microscope (cryosystem, JSM-6301F produced by JEOL Ltd.),
processing the image, and calculating.
[0035] To evaluate printing density, fixability and clogging, a
stencil printing machine, RISOGRAPH (registered trade mark) GR377
(produced by RISO KAGAKU CORPORATION) was used for solid printing,
and the obtained prints were evaluated according to the following
methods. Printing paper used was neutral paper conditioned in an
environment of 23.degree. C. and 50%. The evaluation results are
shown in Table 2.
[0036] Printing Density Evaluation Method:
[0037] Tenth and 500.sup.th prints were sampled, and printing
density was measured at dried solid printing portions of the prints
using a reflection type optical densitometer (RD914 produced by
Macbeth Corp.). When no clogging occurred, printing was further
continued till the 3000.sup.th print, and the printing density of
the print was measured.
[0038] Fixability Evaluation Method:
[0039] On the solid printing portion of the 500.sup.th print, a
crockmeter was reciprocated five times 24 hours after printing, for
sensory inspection of colorant abrasion. Poor fixability is
indicated by .times., and good fixability, .smallcircle..
[0040] Clogging Evaluation Method:
[0041] Printing densities of 10th print and 500th print were
visually evaluated. A case where the printing density of the 500th
print was evidently lower is indicated by .times., and a case where
both the printing densities were equivalent, .smallcircle..
Examples 2-4 and Comparative Examples 1 through 3
[0042] Water-in-oil (W/o) emulsion inks for stencil printing were
prepared as described for Example 1, except that the formulations
listed in Table 1 were used.
Example 5 and Comparative Example 4
[0043] A water-in-oil (W/o) emulsion ink for stencil printing was
prepared as described for Example 1, except that an extender
pigment (calcium carbonate, specific gravity 2.57 (g/cm.sup.3),
average particle size 0.06 /Lm) was added when the colorant was
dispersed.
[0044] These inks were evaluated as described for Example 1, and
the results are shown in Table 2.
1TABLE 1 Example Example Example Example Example 1 2 3 4 5 Oil
Solid Colorant Copper 8.5 8.5 8.5 5.5 phase component
phthalocyanine blue of oil phase Dioxazine violet 8.5 Extender
Calcium carbonate 3 pigment Liquid Resin Alkyd resin 10 10 10 10 10
component Solvent Spindle oil 17.5 10 6 10 2.5 of oil phase AF-5 10
7.5 3.5 7.5 3 Surfactant Sorbitan 2 2 2 2 2 monooleate Water Water
Ion exchange water 43.8 52.3 59 52.3 28.7 phase Organic Ethylene
glycol 7.5 8.9 10 8.9 4.9 solvent Glycerol 39.9 Electrolyte
Magnesium sulfate 0.7 0.8 1 0.8 0.5 Comparative Comparative
Comparative Comparative Example 1 Example 2 Example 3 Example 4 Oil
Solid Colorant Copper 8.5 8.5 8.5 phase component phthalocyanine
blue of oil phase Dioxazine violet 8.5 Extender Calcium carbonate 3
pigment Liquid Resin Alkyd resin 10 10 10 10 component Solvent
Spindle oil 2.5 1 2.5 2 of oil phase AF-5 3 1.5 3 2.5 Surfactant
Sorbitan 2 2 2 2 monooleate Water Water Ion exchange water 62.4
64.9 62.4 60.7 phase Organic Ethylene glycol 10.6 11 10.6 10.3
solvent Glycerol Electrolyte Magnesium sulfate 1 1.1 1 1
[0045]
2 Example Example Example Example Example Comparative Comparative
Comparative Comparative 1 2 3 4 5 Example 1 Example 2 Example 3
Example 4 Colorant Specific gravity 1.74 1.74 1.74 1.43 1.74 1.74
1.74 1.43 1.74 (g/cm.sup.3) Volume (cm.sup.3) 4.89 4.89 4.89 5.94
3.16 4.89 4.89 5.94 4.89 Average particle 1.24 1.24 1.24 1.35 1.24
1.24 1.24 1.35 1.24 size (.mu.m) Extender Specific gravity 2.57
2.57 pigment (g/cm.sup.3) Volume (cm.sup.3) 1.17 1.17 Average
particle 0.06 0.06 size (.mu.m) Volume ratio of pigments 0.1 0.13
0.17 0.15 0.18 0.20 0.24 0.24 0.25 to oil phase Liquid Specific
gravity 0.89 0.9 0.9 0.9 0.91 0.91 0.93 0.91 0.9 com- (g/cm.sup.3)
ponent of Volume (cm.sup.3) 44.4 32.8 23.9 32.8 19.2 19.2 15.6 19.2
18.3 oil phase Water Specific gravity 1.03 1.03 1.03 1.03 1.13 1.03
1.03 1.03 1.03 phase (g/cm.sup.3) Volume (cm.sup.3) 48.5 60.2 68
60.2 65.5 71.8 74.8 71.8 69.9 Average particle size of 0.3 0.3 0.3
0.3 0.3 0.3 0.3 0.3 0.3 emulsion (.mu.m) Weight ratio 1.08 1.63
2.33 1.63 2.85 2.85 3.35 2.85 2.57 (water phase/oil phase) Weight
ratio 1.31 2.1 3.26 2.1 4.23 4.23 5.31 4.23 4.36 (water
phase/liquid component of oil phase) Volume ratio 1.09 1.84 2.85
1.84 3.41 3.74 4.8 3.74 3.82 (water phase/liquid component of oil
phase) Fixability .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. X X X X Clogging .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. X X X X
Printing 10.sup.th print 1.2 1.23 1.18 0.92 1.17 1.18 1.23 0.84 1.1
density 500.sup.th print 1.19 1.22 1.18 0.91 1.15 0.89 0.91 0.56
0.89 3000.sup.th print 1.19 1.23 1.16 0.9 1.12 -- -- -- --
[0046] According to this invention, since the ratio by volume of
the water phase to the liquid components of the oil phase (i.e.,
volume of water phase/volume of the liquid components of oil phase)
is used as an indicator and kept at 1.0 to 3.5, preferably 1.0 to
3.0 at 23.degree. C., aggregation of pigments, particularly
aggregation of organic pigments with non-uniform shapes and a large
average particle size such as copper phthalocyanine blue or
dioxazine violet can be prevented, and a water-in-oil (W/O)
emulsion ink for stencil printing good in printing density and
fixability and not causing clogging can be obtained.
* * * * *